<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<ul class="myul">
    <li>1</li>
    <li class="sunq">2</li>
    <li>3</li>
</ul>
<script>
    var myul = document.getElementsByClassName("myul")[0];
    var li = myul.getElementsByTagName("li");
    console.log(li[1].className);

    var targetUL = document.getElementsByTagName('ul')[0];
    var targetLI = targetUL.getElementsByTagName("li");
    targetLI[1].removeAttribute("class");
    console.log(targetLI[1].className);
</script>
</body>
</html>